Transducer



March 8, 1960 Filed Oct. 13, 1954 rTicrl.

T TTTT/ L. A. PETERMANN TRANSDUCER 7 Sheets-Sheet 1 INVENTOR.

Lac/En H PETER/WAN AZ: %MA,J AM v TELITID QTFOKNE) March 8, 1960 L. A. PETERMANN TRANSDUCER 7 Sheets-Sheet 2 Filed Oct. '13, 1954 IN V EN TOR.

M M H K N E e H .m P w T HAM. N 5 Ln March 8, 1960 A. PETERMANN $928,069

' TRANSDUCER Filed Oct. 13, 1954 7 Sheets-Sheet 3 206 a .25- OUTP INPUT fiflJl/JTGBLE I l F266. 5 f2 REsOA/MCC OUTP T IN VEN TOR. L UCIEN Q. Rrrs'RMn NA/ "g MMMW March 8, 1960 L. A. PETERMANN 2,928,069 TRANSDUCER Filed Oct. 15, 1954 7 Sheets-Sheet 4 INVENTOR. Lumsu H. PETE /mam! HTTaEAIE Y March 1960 L. A. PETERMANN 2,928,069

' TRANSDUCER Filed 001?- 1954 7 Sheets-Sheet 5 INVENTOR. Luz/51v A- PETsRMfi VN March 1960' L. A. PETERMANN 2,928,069

TRANSDUCER Filed Oct. 15, 1954 7 Sheets-Sheet 6 INVENTOR. LUCIE/V H. PETE/VMfih/A/ TTaZA/E f United States Pat m TRANSDUCER- LucienA, Peel-menu, Memchen, NJ, assignor to Gum's Industries, Inc., a corporation of New Jersey Application October 13,1954, Serial No; 461,979

Claims. (Cl. 340-) My invention relates to electromechanical transducers and their usei An important objector my invention ist'o provide a transducer with alower resonant frequency than other transducers. of comparable dimensions.

A further object is to provide a more sensitive trans ducer than other transducers of comparable dimensions.

A still further object of my invention is to provide a transducer which may be produced more economically than other transducers.

Avstill further object of my invention to provide a transducer which will accurately control the frequency of very low frequency oscillatory circuits.

A still further object of my invention is to provide a a transducer which maybe employed as the active element in a phonograph or transcription pickup. v

A still further object of my invention is to provide a transd'ucerwhich may be employed as the active elemerit in aphonograph or transcription record cutter.

A still further object of my invention is to provide a transducer which may be employed as an electro-me chanica'l filter. i V r A still'further object of my invention-is; to provide a transducer which' may beempl'oye'd asa rlay.

A- stillfurther object of my invention is to provide: a

transducerwhich may belemployed as the active element in: a vibrator orcho'pper. I

A- still further object of my invention is to provide a meat inca hydrophojne.

A-- still further object oi my invention isi t'o provide a transducer which may be employed as" the active element in a subaqueous sound projector. V

A still further object-of my invention is to provide a transducer which may be employed as the active: elementin an accelerometer. r

.A still further object ofmy invention is toprovide a transducer which may be employed as the active element' in a; displacement gauge.

A still further object of my invention is to provide a' transducer which may be employed as the active element y invention; is to provide I a 2 application, and in which like numerals are employed to designate like parts throughout the same,

Figure 1 illustrates a method presently used to obtain motion of a flat transducer in flexural mode,

Figure 2 illustrates a method presently used to obtain motion of a cylindrical piezoelectric or polarized electrostrictive transducer in flexural mode,-

Figure 3 illustrates .a method presently used to obtain motion of a magnetost-rictive cylindrical transducer in flexural mode,

Figure 4 is a section of along the line 44, p 7

Figures 5A, 5B, 5C, 5D and 5E illustrate driving field intensities in transducers of varying characteristics.

Figure 6 serves to illustrate and explain the theory underlying my invention,

Figures 6A and 6B illustrate homogeneous and non= homogeneous field distributions in ducers, l 7

Figures 7A and 7B illustrate cross-sections of transducers; made of homogeneous material, and which may be driven electrically in flexural mode by applying the driving voltage on only two electrodes.

the transducer of Figure 3 Figures 7C'and 7D illustrate cross-sections of transducers, made of homogeneous material, and which may not be driven electrically in flexural mode by applying the driving voltage on only two electrodes,

Figure 8 illustrates an embodiment of my invention, Figure 9 is a section of the transducer of Figure 8 along the line 9-9,

Figures 10 and 11 illustrate further embodiments of my invention utilizing piezoelectric or polarized electro strictive material, V r i a Figure 12 illustrates my invention as embodied in a cylindrical magnetostrictive transducer,

Figure 13 is a sectionof the transducer of Figure 12 along the line 13-13, p r V Figures '14 and 15 are employed to explain the theory and operational characteristics of transducers produced according to my invention,

Figure l 6.is an illustration of the equivalent electrical circuit of transducers produced inaccordance with my invention,

'Figure 17 illustrates a method of lowering and continuously adjusting the resonant frequency of transducers produced inaccor'dancevwith my invention," I

Figure 18 illustratesa further method of lowering the resonant frequency of transducers produced in accordtransducer which may be employed as the active element in a so'ni'c cleaning :o r chemical emulsificationsystemi, Other objects" and advanta es or my invention will be ance with my invention,

Figures 19 and 20 illustrate transducers produced in v accordance with my invention, transducer which may be employed as the active ele- Figure 21 illustrates an embodiment of my invention which may be employed as the resonant element of a low frequencyoscillator (this transducer may beiof the tunable type),

Figure 22 illustrates a ance with my invention, employed as" a. band-pass filter (this transducer may be of the tunable type),

Figure 23 illustrates the characteristic frequency response of the filter of Figure 22, v

Figure 24 illustrates the employment of two transducers, produced in accordance with my invention, as a band-pass filter with adjustable band Width,

Figure 25 illustrates the characteristic frequency response of the filter of Figure 24, I

Figure 26 illustrates a transducer, produced in accordance with my invention, employed as a low-frequency, high-amplitude vibrator (this transducer may be of the tunable type x i I v Fig'ures'2 7 and 28 illustrate schematic diagramsofloscillator circuits inwhich transducers, produced inaccordv ance with invention, serve as the frequency control Patented Mar. 8, 1960' magnetostrictive transtransducer produced in accordj n 2,928,069 f o 3 elements (these'transducers may be of the tunable type),

Figure 29 illustrates a twister type transducer, produced in accordance with my invention,

Figure 30 illustrates a transducer, produced in accordance with my invention, employed as the active element in a phonograph pickup,

Figures 31A and 31B are two possible embodiments of a section of the phonograph pickup 'of Figure 30 along the line 3131 of Figure 30,

Figure 32 is a further embodiment of my invention em ployed as a phonograph pickup,

Figure 33 is a planview and Figure 34 is an end view of a torsional type transducer which is produced in accordance with my invention and which requires only two driving electrodes,

Figure 35 is a plan view and Figure 36 is an end view of a further embodiment of torsional type transducer which is produced in accordance with my invention and which requires only-two driving electrodes,

Figure 37 illustrates a transducer-with a continuously adjustable resonant frequency which is produced in accordance with my invention and which may be employed as the tunable element in oscillators, filters, vibrators and like devices, I

Figures 38 and 39 illustrate embodiments of my invention employed as the active elements in accelerometers,

Figure 40 illustrates a transducer, produced in accord ance with my invention, employed as the active element in a hydrophone,

Figure 41 illustrates a microphone utilizing a transducer, produced in accordance with my invention, as the active element therein,

Figure 42 illustrates a transducer, produced in accord ance with my invention, which may be employed as the active element in 'a microphone, hydrophone, projector, loudspeaker or tweeter,

Figures 43 and'44 illustrate the employment of transducers, produced in accordance with my invention, as relays or vibrators,

Figures 45, 46 and 47 illustrate methods of lowering the resonant frequency of transducers produced in accordance with my invention,

Figure 48 illustrates a further embodiment of my invention wherein the displacement of the free end of the transducer is large for a given driving voltage input,

Figure 49 illustratesa transducer, produced in accordance with my invention, employed as a chopper,

- Figure 50 is a lot of the voltage characteristic curve of the chopper of Figure 49, I

Figure 51 illustrates a transducer, produced in accordance with my invention, employed-as a chopper, and

Figure 52 is a plot of the voltage characteristic curve of the cho per of Figure 51.

In the drawings, wherein for the purpose of illustration, are shown preferred embodiments of my invention, the numeral 100 desi nates a piezoelectric or p larized electrostrictive transducer with two portions 100 and 100b, both bonded to a center electrode 102. The outer surface of 100a is bonded to electrode 101 and the outer surface-of 100!) is bonded to electrode 103, such that there is good electrical contact between the portions 100a and 1001: and the electrodes 101, 102 and 103. The combination is suitably affixed to a substantially rigid element 104. However, clamping of the transducer. is not essential to its operation and there are many other mounting means which may be employed with equal. efiect. Terminals 105, 106, and 107 are electrically connected to electrodes 101, 102, and 103, respectively. If transducer 100 is polarized in the directions shown by the small arrows within 100a and 100b, flexural motion will be produced in 100 when voltage is applied between terminals 105 and 107. If the polarization of 100a is in the same direction as that of 100b, flexure of transducer 100 may be obtained by electrically connecting terminals 105 and 107 and applying the voltage between their juncture and terminal 106. If the polarizations of 100a and 10% are as shown in Figure 1 and a direct current voltage versely, under the above described conditions of polariza-' tion directions, a voltage will appear at the terminals designated for each condition of polarization and electrical connection when transducer 100 is subjected to an applied flexural mechanical force or moment in the. direction of arrow 108.

Other methods for making the surfaces of the transducers of my invention electrically conductive, such as reducing the surface by chemical or other means, may be employed in lieu of bonding electrodes to thetransducers surfaces."'Any niethodfwhich produces good electrical contact with thesurface of the transducer, may be employed with transducers produced in accordance with my invention. References to electrodes throughout this specification also include conductive surface mate-' rials obtained by means otherthan deposition of metallic conductive material on the surface of the'transducer.

The numeral 109 designates a cylindrical piezoelectric or polarized electrostrictive transducer with two pairs of electrodes, electrodes 110 and 111 being one such pair The numeral "114 designates the electrical connections from electrodes 110 and 112 to terminal 115 and the numeral 116 1de signates the electrical connections from electrodes 111 and 113 to terminal 117. Transducer 109 is suitably afl'ixed to substantially rigid element 118. However,

clamping of the transducer is not essential to its operation and there are many other mounting means which may be employed with equal effect. The polarization of trans ducer 109"is in' the direction shown by the small arrows on transducer 109. Reversal of this polarization by 180 degrees will produce the same fiexural results as herein described. If the alternating voltage is applied between 7 terminals 115 and 117, transducer 109 will flex in the y directions indicated by arrows 119 and 120. Ma directcurrent voltage is applied between terminals 115and 117 as shown in the figureftransducer 109 will flex-and remain in the flexed position after the voltage source is removed and until the charge leaks ofi. Conversely, under the abovedescribed conditions of polarization direction, voltage will appear across terminals 115 and 117 when transducer 109is subjected to an applied flexural mechanical force or moment in the direction of arrows 119 and 120.

Transducers and 109wjill flex at a ratedetermined by the frequency or. time dependence of the alternating voltage applied to theirrespective electrical terminals. Conversely, the voltage appearing-across said electrical terminals will be of the same frequency or time dependence as that of mechanical force or moment applied to 122a and 123a. The time dependence of this flexure is determined by the frequency'or time dependence of the flowing alternating current. Conversely, alternating currents willflow through opposed windings 122an'd 123 it there is a direct current fiowin bias windings 122a and 123m when'transducer 121 is subjected to mechanical force or moment in the directions indicatedby arrow 125. The

escapee frequency or time dependence of. suchcurrent flow will the flexural motion of each elementary portion of spe cially shaped transducers and provide very low resonant frequencies of vibration for transducers of very small dimensions. In particular, transducers of the shapes and physical characteristics illustrated-in Figures 33 through 136 and 48 will vibrate at the lowest possible resonant frequericies for a givenoutside dimension. Fora given ma terialand set of dimensions, transducers, produc'edfac'cording to my invention will vibrate at lower resonant frequencies than. may be obtained by any other method.

'Thenecessary and sufficient conditions for the production, by the use of electric or magnetic fields, of flexural vibration of a transducer composed of a completely homogeneous material and having only two driving electrodes one single driving winding are: first, the applied (driving) dynamic field (electric or magnetic) inthe cross section of the transducer shall not be homogeneous (shall be nonhomogeneous) over the entire cross-section; and second, the absolute instantaneous values: of the field (electric or magnetic) at symmetrical points about the neutral axis shall not be equal. My invention directs itself to those transducers which meet these conditions.

The neutral line in a. transduceris that line which does nothchangeits length. during. flexure of the transducer. The'neutral surface is the surface which contains the neutral line and is perpendicular to the direction ofrflexure. The. intersection of the neutral surfacewith the crosssection of the transducer isthe neutral axis.

Although there are many ways to obtain non-homo.- geneous dynamic fields in piezoelectri -polarized electrostrictive or magnetostrictive transducers, such. as the use of more than two electrodes or a single driving winding,..

6 is no current flow anywhere in transducer 437 and consequently, there; is no current flow in area; A. The dynamic driving'field is'produced by helical windings 438 which are evenly distributed along transducer 437. Curl B is equal to zero everywhere in 437 and within enclosed area A.

I Bds=Jf curl Ede-= 0 1-2-34 7 Portions 2-3 and 4--1 of 437 are such that Bds is equal to zero. (B perpendicular to ds.) We obtain is equal to zero; From which, Bl/BZ is equal to 3--4/ 1-2; and if 3"4 is-not equal to 1--2,-th'en Bl is not equal to Bland the field is-non-homogeneous. Figure 6B is a longitudinal section of transducer 437.

Figure 6A showsv a longitudinal section of magnetostrictive transducer 435 which is of homogeneous material. Longitudinal axis 435a is a straight line and the cross-section of transducer 435-is symmetrical to some line perpendicular to 435a. In transducer 435', 3-4- is equaifto 1 -2 and, therefore, B1 is equal to B2 and the field in 435'ishomogeneous. e

The driving dynamic instantaneousfield 126 of Figure 5A is homogeneous andtherefore, therewill be no flexure, electromechanically produced, in a transducer of this cross-section .andof homogeneous piezoelectric, polarized electrostrictive ormagnetostrictiveproperties if only two driving electrodes or a single driving Winding are used. The driving'dynamic fields (instantaneous) 127 and 128 ofFigures 5B andSC are not homogeneous and if they non hcmogeneous material; and like methods, my invention teachesthe' obtaining of non-homogeneous, dynamic fields by the correct and proper shaping of the transducer. V

Only two driving electrodes are required for a piezoelectric or polarized electrostrictive transducer and only a single driving winding is required for a rnagnetostrictive transducer.

Transducers shaped and produced in accordance with my invention will contain non-homogeneous dynamic driving fields even though the material comprising the transducer is homogeneous in all respects.

For the electric field, consider thealaw of the conservation of flux; We have div E equal to lip-{where piis the density of charge, It is a constant, and E' is the electric field. 'Further, the field is. always perpendicular to an The electrodes ofthe transducer are equipotential' surfaces as long as they :are much smaller in, size. than. the, wavelength of: the. applied alters For the usual sizes of transducers with I equipotential surface.

frequencies),, curl, B eq al, to. kj; where B is the mag-' netic induction, -k is al; constant and j. isthecurrent density. Transducer 437, shown in Figure 6B, contains enclosed area.v A. Disregarding eddy currents, which may be reduced considerably by conventional methods, there are not symmetrical-about. the neutral axis of transducers of this cross-section= andof homogeneous material and of homogeneous"piezoelectric, polarized electrostrictive or magnetostrict-ive properties, the transducers can be excited in flexuralvibration, by electro-mechanical means In Flgure 5D, magnetostricti-ve transducer is suitably affixed to' substantially rigid body 138 and has windings 136 and 137 wound around the outside; 136 being the driving winding and 137 being the bias winding. The neutral. axis is designated as 139 and the driving dynamic instantaneous field isas indicated by the arrows in the figureifi Under-these conditions transducer 35 will not Figure: 6 serves-to. illustrate the positions ofthe neutralline, neutral surface, and neutral axis with respect tothe direction-of fiexure; The numeral 130 designates the,

neutral line;-the numeral. 131' designates the neutral surface, the numeraPl-32 designates theneutral axis, the

numeral 133 designates a substantially rigid body to which transducer 129'- is suitably affixed and the numeral 134' designates the direction of'fiexure. Transducers produced according. tomy'invent ion' need not be rigidly attached at any particular. point but'maybe suitably held at many different. points without adverse-151' affecting the operation" of the transducers? in e'l'ectr'o rnechanical: flexural vibration;

In Figures 7A and7B, fields and 146 are not homogeneous and: are: not symmetrical about their respective neutral axes 145a% and 146a and, therefore, flexure can be produced with only twoelectr'odes in transducers ofhontogeneous rnate'rial and of. such cross-sections and applied field distributions. 'Field' 1 47, shown in Figure 7C; is homogeneous and symmetrical about neutral axis 147a and, therefore, flex-urecannot be produced by electromechanicah means in, a homogeneous? transducer ofthis cross-section and driving field distribution if only two electrodes are employed. Field 148, shown in Figure 7D, is not homogeneous butit is symmetrical about neutral axis 148a and, therefore, fiexure cannot be produced by electro-mechanical means in a homogeneous transducer of this cross-section and driving field distribution if only two electrodes are employed.

My invention is concerned with obtaining non-homogeneous distribution of the applied driving dynamic field and its non-symmetrical distribution about the neutral axis so that transducers of homogeneous material may be caused to vibrate in flexural mode with only two driving electrodes or a single excitation winding. No matter how the driving dynamic field distributions (electric or magnetic) are obtained, flexural vibration will be obtained by electro-mechanical means as long as the necessary and suflicient conditions of non-homogeneity of field distribution and non-symmetry about the neutral axis are fulfilled. The driving dynamic field distributions illustrated throughout the drawings are instantaneous field distributions which vary in accordance with the alternating voltage applied. However, if the instantaneous field distribution satisfies the requirements of flexure at any one instant, it will satisfy the conditions at all instants, the time and space dependence of such fields being independent functions which are multiplied in the steady state expression of these fields.

Figures 8, 9, 10 and 11 illustrate some embodiments of my invention as applied to piezoelectric or polarized electrostrictive transducers of homogeneous material. Transducer 149 will flex in the directions indicated by arrow 154 if an alternating voltage is applied across terminals 152 and 153 which are electrically connected to electrodes 150 and 151 respectively. The triangular cross-section is illustrative of the method of obtaining a nonhomogeneous distribution of the applied dynamic driving field which is non-symmetrical about the neutral axis of the transducer. Other cross-sectional shapes such asregular and irregular polygons and non-symmetrical curved shapes of various curvatures may be employed equally effectively.

I choose to define transducers of the type depicted by transducer 155 of Figure 10 as split cylinders, a split cylinder being a cylinder with a small portion parallel to the longitudinal axis removed. Transducer 155 will vibrate in flexural mode in the directions indicated by arrows 160 if an alternating voltage is applied across terminals 158'and 159 which are electrically connected to electrodes 156 and 157 respectively.

- Transducer'l61, which is a segment of a cylinder, will vibrate in flexural mode in the directions indicated by arrows 166 if an alternating voltage is applied across terminals 164 and 165 which are electrically connected to electrodes 162 and 163 respectively. Transducer 161 may also be considered as a split cylinder and it is possible" to drive it in a flexural vibration wherein thedisplacements are distributed in the manner depicted in Figure 10. Portions of'other types of curved surfaces will-vibrate in similar fashion to that described for transducer 161.

Conversely, since all transducers are electro-mechanical devices, an alternating voltage will be developed across the terminals which are electrically connected to the electrodes when a mechanical stress is applied in the direction of flexural vibration. The time dependence of the alternating voltage, thus produced, is determined by the time dependence of the mechanical flexure, iust as the time dependence of mechanical flexure is determined by the time dependence of the applied voltage.

Transducer 167 is a split cylinder of the magnetostrictive type with driving winding 168 and bias winding 169. Numeral 170 designatesa block of high permeability magnetic material which is employed to close the magnetic circuit, that is, todecrease the reluctance of the circuit. A direct-current biasing current is caused to flow through 169 and transducer 167 will vibrate in flexural mode in the directionsindicated by arrows 171 when an alternating current is made to flow through winding 168. Conversely, so long as the bias current is maintained, an alternating current will flow in winding 168 when a vibrating mechanical force is applied to transducer 167 in the direc-' tion of arrows 171.

As I have stated previously, my invention applies to transducers of the piezoelectric, polarized electrostrictive and magnetostrictive types and the illustration of a particular shape in one of the types but not in the others does not mean that the other types may not be produced in that particular shape. It should be clearly understood that transducers of all these types may be made in all the shapes discussed. While it is not necessary to the operation of my invention, it should be noted that in all the cases discussed the material comprising the transducer is completely uniform and homogeneous. The necessary and sufficient conditions for vibration in flexural mode with only two driving electrodes or a single driving winding apply when the material of the transducer is uniform and homogeneous. If the materialis non-homogeneous, the conditions may be sufiicient but not necessary.

In order to further explain the theory underlying my invention, it is advisable to consider transducer 172 of Figure 15 which has a length equal to 21 and a thickness to 2. Assume that the curve along 2l is smooth, that the cross-section is the same throughout the transducer and that 21 is greater than t. Then the resonant frequencies in flexural mode f are given by the expression:

where ,z=number depending on the harmonic considered and the type of support of the transducer (z=2.635 for the fundamental flexural mode with the transducer unclamped) E=Youngs modulus of the material being used l'zmoment of inertia of the cross-section With respect to the neutral axis of the cross-section =specific gravity l=half the length of the flexing transducer s=cross-section of the flexing transducer.

For a given mode (either fundamental or harmonic) and a given material, z, E, and p are constants and l=k S,

*where k is the radius of gyration, we obtain the expression: I

T f constant f constant;

12 f -constant In the case shown in Figure 14, in which transducer 173 is a split cylinder or in any other case in which the cross-section 174 is a rectangle, we obtain the expression:

where t is the cylinder wall thickness; from which 2 f constant For barium titanate, the constant is found to be equal to 1:105 cm, l=16 .6 cm.

and if t=0.1 cm. t=0. 25 cm.

driven at relatively low voltage for large amplitudes of vibration.

Split cylinders'have a very high figure of merit, Q, of the order of 1,000 to 3,000 at frequencies from to 1 ,000 cycles per second. This is. much higher than circuits, employing purely electrical components, yield at these low frequencies. The value of Q may be varied by clamping creasingthe friction or by similar means. The lowest value of damping is obtained when the transducer is clamped at the nodal surfaces and the electrode leads are connected on the nodal surfaces. The position of the nodal surfaces varies with the shape of the transducer and may be calculated from the particular solution of the differential equation of linear flexure corresponding to the particular mode and type of boundary conditions, under study. The Q of a giventransducer may be adjusted to almost any value-between 0.5 and 3,000 (approximately). The resonant frequency for a given transducer of .a particular material and dimensions will vary by approximately 15% at these extreme valuesof Q. l

Figures 17 and 18 illustrate two methods of lowering the flexural mode resonant frequency of a given transducer. Transducer 179 hassecurely afiixed thereto threadedelements180 on which are threaded masses 181.

v The further away masses 181 are from transducer 179,

the more the resonant frequency of the transducers flexuralmode is displaced. from the or-iginal resonant fre quency. The resultant resonant frequency is lower or higher than the original resonant frequency depending on the direction of threadedelernents 180. with respect to. the motion of transducer-179 in flexural: vibration;

Transducer 182 has; atfixed thereto masses 183; These masses 183 are not adjustable and the flexural resonant frequency is likewisefixed. However, the frequency is lower than it would be if the same transducer were unloaded.

Transducers 184 and 186 are producedacc'ording to my invention and will vibrate in flexural mode when driven by only two electrodes. In thecase of 184, the electrodes, are designated 188 and 189' and in thef'ca se of 186, the electrodes are designated 190 and 191'. The nodal sur-. faces of transducer 184 are designated by numeral 185 and those for transducer 186 are designated by numera1187.

: Transducer 192 maybeemployed as-the frequency control element of a low frequency oscillator. Numeral 193 designates the driving electrode, numeral 194' designates the feedback electrode and numeral 195 designates the electrode which. is maintained: at groundpotential. The

, leadsfor the input and. output connectionsare 3.660111? the transducer, or by adding mechanical, loads, or by ima mersing all or part of the transducer in a liquid, or. by inplished at the nodal surfaces 200. Curve 201 is a typical; output/input against frequency plot. of thercsponse of transducer 196.

Transducers 202 and 203 are shown connected as; a band-pass filter with adjustable resonant frequencies. Masses 204 and 205 may be moved closer to or further away from transducers 202 and 203 in order to vary the, resonant frequency of each transducer. Curve 206 is a typical output/ input against frequency plot of the response. of the combination of transducers connected as shown in Figure 24.

Transducer 207 is shown connected as a low-frequency: high-output vibrator. Coil 208 serves to balance, out the static capacitance of transducer 207 and to match the: equivalent electrical impedance of transducer 207 to the; output impedance of gener-ator'209 at the-resonant fre-rquency. The frequency of generator 209 is adjusted. to: the resonant frequency of the flexural mode at which We, desire to have transducer 207 vibrate.

Transducers 210 and211 are shown as the control elements of typical electronic oscillator circuits. Because.

of the low resonant frequency of these transducers in the flexural vibrations of' all elementary portions and the shape of the transducer produce the twisting motion.

Transducers of the type of. transducer 212 are useful as microphone elements. The'electrodes are applied to faces" 214 and 215 and when an alternating voltage is applied between them, transducer 212Iwillvibrate as indicated by electrodes 219 and 220. Conversely, if a voltage iszapplied across electrodes 219 and 220, needle 218 will vibrate in accordance with the time dependence of the applied voltage. Figure 31A illustrates a single type pickup or cutter needle 218 and Figure 31B illustrates a dual type pickup needle which may be employed for use with phonograph records and transcriptions which require-elements of different tip-radius; When the dual pickup elemerit, as illustrated in Figure 31B, is employed, transvarious methods of adjusting the resonant frequencyof the' flexural vibrations of the transducers which are described in. this specification: may be employed to adjust the frequency of transducers of the; type of transducer 192.

Transducer 196 is shown connected to serve as a bandpass filterwherein the input is applied-between electrodes 197 and 199 and the output isobtained across electrodes 198 and 1 i mum amn na d hi hes Q s obs ducer 216 is pivoted about point 221 so that eitherpickup needle 2181 or'2'18,2; is in contact wi'th'the record groove or transcription groove which is to be reproduced by the system. l

Transducer 222 is the active element in a dual needle type of phonograph or transcription pickup to which needles 223 and 224 have been suitably affixed. The

combination is pivoted within clamp 229 so that the re-' quired needle is in contact with the .record or transcription to be reproduced. Electrical'output connections are made to terminals 227 and 228'which are electrically connected to electrodes 225 and 226 respectively.

Transducer 230 is a torsional type transducer. inithe" shape of a cylinder with electrodes 231 and 232 on the surfaces of said transducer and a helix 233 cut along the surface of 230. When an; alternating voltage is applied across electrodes 231-and' 232, transducer 230 will twist, in the directions indicated-by the arrows 234.' Transducer 235 is similartotransducer 230' except that helix 238, which is cut in transducer 235, does not extend along the whole length oftransducer 235. If 'an alter nating voltage is applied between electrodes 236 and 23.7,

transducer 235 will twist in the directions indicated by arrows 239.

Transducer 240 is a tunable very low frequency reso nant element which may be employed inall applications which require a tunable element. Transducer 240 is clamped between rollers 241 and 242 which are suitably fixed in holder 244. Rollers 241 and 242 are coated with a material 241a, the stiffness of which is chosen to permit obtaining the mechanical Q which is desired. This coating material may be made electrically conductive or it may be insulating, according to the requirements. If they are conductive, they may be used for the electrical connections to electrodes 245 and 246 with which they are in contact. The clamping action of rollers 241 and 242 fixes the nodal lines at their line of contact with transducer 240 and this in turn, fixes the resonant frequency, as determined by the distance between the lines of clamping and the free ends of transducer 240. By adjusting knob 243, the position of clamping is shifted on transducer 240 which moves between rollers 241 and 242, and thus, the resonant frequency is adjusted. External electrical connections are made (when 241a is of insulating material) to terminals 247 and 248 which are electrically. connected to electrodes 245 and 246, respectively.

Transducer 249 is the active element in an accelerometer or strain gauge. Mass 251 is applied to one end of 249 and the other end is clamped to substantially rigid body 250. In some applications, mass 251 is not required, in which case the mass of the transducer 249 itself serves as the inertial element. External electrical connections are made to terminals 254 and 255 which are electrically connected to electrodes 252 and 253, respectively.

, Transducer 256 is the active element in an accelerometer, strain gauge or pressure gauge. Mass 257 is affixed to one end of transducer 256 while the other end is suitably clamped to substantially rigid body 258. External connections are made to terminals 261 and 262 which are electrically connected to electrodes 259 and 260, respectively.

Transducer 263 is a subaqueous hydrophone or projector. Electrodes 264 and 265 are respectively connected to terminals 266 and 267 to which the outside electrical connections are made. contain liquid 269 which is employed to damp the vibration of 263. In some applications, only a single membrane is required, in which case, it serves to prevent the outer liquid from entering the transducer. The numeral 270 designates an air space which is sealed from the outer liquid by membranes 268 and at both ends of 263.

Clamps 271 are applied to transducer 263 along the nodal surfaces and are suitably aflixed to substantially rigid body 272.

Transducer 273 is the active element of a microphone. One end of 273 is attached to pin 274 which in turn is attached to diaphragm 275. The other end of 273 is clamped at point 276 to housing 277. When sound waves strike diaphragm 275, pin 274 causes transducer 273 to vibrate in flexural mode and an electrical voltage appears across terminals 280 and 281 which are electrically connected to electrodes 278 and 279, respectively. Conversely, the same embodiment may be employed as a loudspeaker or tweeter. In which case, the application of alternating voltage at audio frequencies across terminals 280 and 281 will cause diaphragm 275 to vibrate at audio frequencies.

Transducer 282 in the embodiment illustrated may be employed as a microphone, hydrophone, projector, loudspeaker or tweeter. The numeral 283 designates an acoustic isolator such as cork, corprene or like material which serves to prevent transmission or reception of sound in the inner portion 'of the transducer 282. Electrical connections are made to terminals 286 and 287 which are electrically connected to electrodes 284 and 285, respectively.

Transducer 288 is illustrated as a relay wherein terminals 293 and 294 are rigidly'attached to one end of 283 andmakecontact with, terminals 292 and 295 during Membranes 268 serve toflexure. When contact is closed between terminals 292 and 293, it is open between 294 and 295 and vice versa. Transducer 288 is caused to flex by the application of a voltage across terminals 296 and 297 which are electrically connected to electrodes 290and 291 respectively. The end of transducer 288 carrying terminals 293 and 294 will have the maximum displacement amplitude because the other end is suitably aflixed to substantially rigid body 289.

Transducer 298 is a relay which closes two circuits when it is flexed in one direction and opens the circuits when it is flexed in the opposite direction. Transducer 298 is caused to flex when a voltage is applied across terminals 301 and 302 which are electrically connected to electrodes 299 and 300, respectively. When transducer 298 flexes outward, contacts 303 and 305 are electrically connected and contacts 304 and 306 are electrically connected. When the transducer 298 flexes inward, the contacts are broken and the circuits are opened. More than two sets of contacts may be opened and closed in this manner since a plurality of such contacts may be aflixed to the transducer along the flexing cross-section. The relays depicted in Figures 43 and 44 may be operated with either a DC. or an AC. voltage. The maximum amplitude of displacement is attained when the AC. frequency is equal to the transducers flexural resonant frequency.

Transducers 307, 308, and 309 are illustrative of various methods of increasing the mass-compliance. of transducers of given dimensions in order to lower the resonant frequencies. These transducers may be employed as the active elements in any of the applications for which the transducers contemplated by my invention may be used.

Transducer 310 is clamped to substantially rigid body 315 and will flex in the directions indicated by arrow 316 when a voltage is applied across the terminals 313 and 314 which are electrically connected to electrodes 311 and 312, respectively. The motion will be of particularly large amplitude for transducers of small dimensions.

Transducer 317 is clamped at its nodal surfaces 325 and is employed as a chopper. The time dependence of its output wave-form across terminals 326 is illustrated by curve 327. Curve 327 is typical of the output when a direct-current voltage is applied across terminals 324. With no voltage applied to terminals 324, terminal 319,

which is bonded to electrode 318, is in contact withterminal 320, and terminal 322, which is bonded to electrode 321, is in contact with terminal 323. When a direct-current voltage of the proper polarity is applied across terminals 324, the transducer 317 flexes inward and breaks the contacts between terminals 319 and 320 and between terminals 322 and 323; After the charge is removed because of current flow in the circuit associated with terminals 326, the transducer 317 returns to its original position and the cycle starts again.

Transducer 328 is a chopper with electrodes 329' and 330. Terminals 331 and 332 are bonded to electrodes 329 and 330, respectively. In the unflexed position, terminals 331 and 332 are in contact with spring contacts 333 and 334 respectively. When a direct-current voltage of the proper polarity is applied to terminals 335, spring contacts 333 and 334 remain in contact with terminals 331 and 332 for a longer period than if the contacts 333 and 334 were not on springs and'the consequent output waveform across terminals 336 is of the shape shown by curve 337. After-the contact between 333 and 331 and between 332 and 334 is broken, the charge is removed from transducer 328 because of the current flow in the electrical circuit associated with terminals 336 and transducer '328' returns to its original position and the cyclestarts again.

While I have described my invention by means of specific examples and in specific embodiments, I do not wish to be limited thereto for obvious modifications'will occur to those skilled in the art without departing from the spirit and scope of the invention.

Having thus described, my invention, I claim:

1. A subaqueous sound unit comprising a split cylindrical electro-mechanical transducer; a P i of membranes aflixed to the surfaces of said transducer such that V a nodal surface thereof.

5. A subaqueous sound unit as described in claim 1 wherein the material comprising said transducer is a polarized I electrostrictive ceramic.

References Cited in the file of this patent UNITED STATES PATENTS Pierce Mar. 11,1930 Sawyer Apr. 28, 1931 Sawyer Apr. 28, 1931 Pierce Oct. 11, 1932 Scott Dec. 7, 1937 Melhose June 21, 1938 Williams Dec. 26, 1944 Peek Mar. 9, 1948 DHeedene Ian. 11, 1949 Gray NOV. 1, 1949 Gravley July 18, 1950 Thuras Sept. 5, 1950 Williams Aug. 21, 1951 Mason Aug. 19, 1952 Williams 'Oct. 14, 1952 'Baerwald Nov. 17, 1953 Brown Oct. 4, 1955 Harris Nov. 5, 1957 

